Comparison of the luteinizing hormone-sensitive adenylyl cyclase of the pig ovarian follicle and corpus luteum and its susceptibility to in vitro hormone-dependent desensitization.
The hormone responsiveness of the adenylyl cyclase of pig ovarian follicles or corpora lutea was examined. Adenylyl cyclase activity was assayed in 10,000 x g membrane fractions that had been prepared with or without (control) a urea extraction. In control luteal membranes there was little stimulation (less than 2-fold) or adenylyl cyclase by saturating ovine (o) LH, hCG, or (-)isoproterenol in the absence or presence of 10 microM GTP. However, in urea-treated luteal membranes, a 2- to 3-fold stimulation of adenylyl cyclase was caused by saturating oLH or hCG, and a 4- to 5-fold stimulation by (-)isoproterenol; the marked stimulation by the gonadotropins was only observed if 10 microM GTP was added. In follicular membranes, a 3- to 4-fold stimulation of adenylyl cyclase by gonadotropins was observed regardless of whether GTP was added or the membranes had been urea extracted. Stimulation of adenylyl cyclase by (-)isoproterenol was always less than 2-fold in follicular membranes. The binding affinity for [125I]hCG was similar in control follicular and luteal membranes, but there were approximately 10-fold more [125I]hCG-binding sites in follicular compared with luteal membranes. The binding affinities and number of receptor sites were not significantly changed by urea treatment. The ED50 values for hCG or (-)isoproterenol were the same in follicular and luteal membranes and were uneffected by the addition of 10 microM GTP, but the ED50 for oLH was 3-fold lower in follicular than in luteal membranes. GTP caused a dose-dependent increase in adenylyl cyclase activity in luteal and follicular membranes, and both tissues had the same ED50. A saturating hormone concentration resulted in an approximately 2-fold decrease in the ED50 for GTP. In vitro hCG-induced desensitization of the hCG-responsive adenylyl cyclase was 31% in follicular membranes, but only 11-15% in luteal membranes. Hormone-induced desensitization was not increased in incubations of luteal homogenate or membranes plus cytosol. These results establish the existence of a LH/hCG-sensitive adenylyl cyclase in the pig corpus luteum and indicate that the G-protein and catalytic moieties of the follicular and luteal adenylyl cyclase complex are functionally the same, but some difference exists in the way the LH/hCG-receptor in the two tissues interacts with the G-protein/catalytic complex.
Ekstrom
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RC
Department of Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611.
Hunzicker-Dunn
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M
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D003338:Corpus Luteum / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D005260:Female; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000494:pharmacology*; D006080:Ovarian Follicle / Q000201:enzymology*; D013552:Swine; D014508:Urea / Q000494:pharmacology
D006063:Chorionic Gonadotropin; D006160:Guanosine Triphosphate; D014508:Urea; D007986:Luteinizing Hormone; D000262:Adenylyl Cyclases; D007545:Isoproterenol